The invention relates to a connector assembly for a transformer box for providing power to multiple output devices and more specifically to a transformer box having connection blocks to facilitate connections with improved safety and accessibility.
Environmental lighting systems typically operate by providing low voltage to a number of lamps which are positioned to enhance various features in the environment, such as buildings, statues or trees, or to illuminate walkways or open areas for safety. The low voltage, usually 12 volts, is produced by one or more transformers that are connected to a 120 VAC source and positioned within the area covered by the lighting system in a way to ensure a supply of stable voltage levels as well as to operate efficiently. An important consideration when designing a lighting system is light output and lamp life, both of which are optimized when each lamp is operated within a relatively narrow voltage range, e.g., 10.5 to 11.5 volts. Because the light fixtures are usually positioned at varying distances from the transformer box with differing numbers of fixtures on different cables, the voltage requirements for any given cable may differ. Cables to lamps at the greatest distance from the transformer and/or having a greater quantity of lamps will require an initially higher output voltage and/or a heavier gauge of cable to compensate for voltage drop over long stretches of cable and multiple lamps. The physical size of the cable on the 12 volt secondary side can become very large when a cable run requires a high wattage load, such as would be needed for a long path or driveway. Basic electrical theory dictates that the cable conductors on the 12 volt side of the transformer will be much larger than the conductors on the 120 volt primary side. In order to reduce the supply voltage down to a safe 12 volts, the amperage must be increased by a factor of ten. In theory, the cable gauge to carry 300 watts at 12 volts (25 amps) should be 10 times the thickness of the cable from the 120 volt source (2.5 amps.) To correctly account for this relationship, the low voltage connector in a terminal box should be able to accommodate large gauge cables. In conventional outdoor lighting systems, however, this is not the case, and the available connectors do not provide adequate physical openings to securely receive large gauge cables. Another consideration in the lighting system design is centering of the wattage load in order to minimize cable runs, also to avoid excessive voltage drops for efficient use of the supply voltage.
Most existing transformer boxes were designed and built for industrial applications. Although the basic functionality of a transformer box has not changed for many years, there is now a heightened awareness of safety and visual accessibility issues that exist when they are used in a public, commercial, or residential setting, such as in environmental lighting systems. An aspect of environmental lighting systems that creates a particular safety issue is the aforementioned need to center the transformer within a lighting zone for balanced distribution of power. This means that the transformer may be located in a position that is not as easily secured as might be, for example, a service cabinet or closet on the side of a building or garage. Thus, while efforts are usually made to locate the transformer inconspicuously, outside of direct view, they may, nonetheless, be accessible to individuals, including children. Thus, it is important to ensure that wires leading to and from the transformer be firmly secured.
Lighting systems are typically installed by professional installers who will need ready access to the transformer""s interior connection points. In existing systems, these connection points are often plastic conduit sleeves into which the bare cable wire is inserted and held in place by a flat-top set screw. Set screws are located within a covering made of plastic or other insulating material to prevent inadvertent contact with metal which may be conducting electricity. In a typical low voltage lighting installation, there are several field cables running into a single terminal connection. It can be difficult for the installer to insert the large gauge, often-times stiff wires into the narrow openings. Further, the set screws, which are fairly small, are recessed within the protective material, so the screwdriver must be inserted into an opening in the plastic, making clear visual confirmation of the connection difficult. Most terminal connectors are of a blind type which do no allow the installer to visually confirm the connection by seeing the conductors pass under the set screws. Without a solid connection, arcing and overheating can occur. Although the voltage may be low, the current can be as high as 50 amps. Loose or inadequate metal-to-metal connection with the field wire can be particularly hazardous since the circuit protection in the transformer or main house circuit breaker will not detect an overheated terminal connection because it does not cause a short or an excessive amperage to trip the breaker.
Since the installer is generally well-versed in safe handling of electrical conductors, and since he or she will be doing most of the installation with the system disconnected from a live voltage supply, safety concerns are not as much of an issue as they might be for the uninitiated homeowner or curious child after the lighting system is operational. Thus, the installer may consider the conventional safety features to be obstacles to making secure connections. Regardless of inconvenience to the installer, safety precautions must be taken to avoid accidental electric shock once the 120 VAC is connected.
For the reasons described above, there remains a need for a transformer box construction that allows for easy and secure connection of a lighting system in the smallest-possible physical size enclosure while providing protection against electrical shock for untrained persons who may intentionally or unintentionally gain access to the interior of the transformer box.
It is an advantage of the present invention to provide a transformer box connector that allows for easy and secure insertion of electrical wires.
It is a further advantage of the present invention to provide a transformer box connector with a hinged cover that protects against direct contact with bare wire or an exposed connector after the system is operational, thereby helping to limit the possibility of severe injury from electrical shock.
Another advantage of the present invention is to provide a transformer box connector that is safe, compact, and simple-to-use.
Yet another advantage of the present invention is to provide a terminal connector that provides means for visual confirmation of a connection.
In an exemplary embodiment, the transformer box connector is encased within a transformer box. The transformer box has a hinged door and an interior volume for retaining a transformer housing. A transformer and other components can be located underneath the housing. The hinged door includes a lip which attaches to the latching mechanism mounted on the side of the transformer box for securing the hinged door. The transformer box will preferably be made of a stainless steal or other similar material so the transformer box will be protected from outside elements. The transformer box is supplied standard household power of 120 VAC via an electrical cable or power cord.
In an exemplary embodiment, the transformer box connector comprises a terminal block retainer mounted on a housing located in the interior of the transformer box. The terminal block retainer has a hinged cover that is pivotally attached at the rear corners of the terminal block retainer. In one embodiment, the hinged cover can be lifted and slide downward from the top of the rear corners so that the hinged cover will be locked into place. In another embodiment, the hinges are configured to provide a catch or lock which allows the cover to be temporarily locked in place in the up position. The hinged cover includes a plurality of openings in its top to allow a screwdriver or fastening device easy access to lower voltage terminals to tighten the setscrew without lifting the hinged cover, thereby eliminating direct contact with an electrically hot wire or connector. The hinged cover will preferably have a plurality of slots or openings in the sides or front corners to allow fastening screws to restrict movement of the hinged cover for additional safety measures.
In one embodiment, the terminal block retainer has a plurality of insulating ribs or partitions. Within each insulating rib of the terminal block retainer, a generally cube-shaped terminal block is mounted to provide for insertion of electrical wires. The insulating ribs separate each terminal block from the other to electrically isolate each connection. The insulating ribs also guard against inadvertent contact with one terminal block when inserting or removing a wire at a neighboring block. The terminal block retainer is a molded plastic or polymer, preferably a material that is tolerant to high temperatures.
Each terminal block is preferably formed from a die cast aluminum or other similar material, but may be machined or molded. Each terminal block has a front face and a top, both having bores formed therethrough which intersect within the block. The front face bore can be formed as a circle, but is preferably off-circular to provide a large diameter opening near the bottom of the block to facilitate insertion of wires. The top bore is internally threaded from the top, preferably all the way to the bottom of the hollow interior of the block. A setscrew is screwed into the top bore for locking wires in place after insertion into the front face bore. In the preferred embodiment, the top to bottom threading of the top bore allows for the setscrew to be adjusted in accommodating from a single thin wire to a bundle of heavy gauge wires.
Each terminal block is mounted to the terminal block retainer by a planar member that is formed at its base and extends horizontally therefrom. A fastening member attaches to the planar member. The fastening member can be configured as a fastening screw or a threaded fastening post, and is formed from a conductive material to provide an electrical conduction path from the terminal block to the transformer taps. The fastening screw or post is inserted through the terminal block retainer and an opening in the housing opening, and is secured at its end by a receiving nut once other connections have been completed.
In an exemplary implementation, an electrical wire from a transformer tap is attached to the fastening member by a round washer crimp or a similar fastening means. The round washer crimp, which attaches to the end of the electrical wire, has a washer portion with a diameter adapted to fit over the fastening member. The washer portion of the round washer crimp is slid onto the end of fastening member and upward until the top portion is butted against the circular shaft of the terminal block retainer. The round washer crimp is secured in place by the receiving nut so that the round washer crimp and the electrical wire is secured between the circular shaft and the receiving nut.
In alternate embodiment, a pair (or more) of retaining sleeves can be used to secure the housing against the terminal block retainer. A retaining sleeve is inserted over the fastening member and the circular shaft of the terminal block retainer on at least one shaft location on either side of a centerline bisecting the terminal block retainer. The retaining sleeves provides upward force against the upper face of the housing to ensure a tight fit between the terminal block retainer and the housing. The receiving nut provides for securing the retaining sleeves in place.
In a second embodiment, the terminal block retainer has partitions extending upward and downward from a plane in which the terminal blocks are positioned. Each cavity or cubicle defined by the partitions has a front wall with an opening formed therein. The terminal blocks have an upper connector portion for retaining wire ends for wires exiting the transformer box. A lower connector portion extending downward from a planar center section is substantially an inverse mirror image of the upper portion and provides connection to wire ends leading from the transformer. In a manner similar to the upper portion of the terminal block, a set screw inserted into a threaded bore perpendicular to the wire ends is used to secure the wire ends inserted into the lower portion of the terminal. A groove extends along the sides of the planar center section to interfit with a corresponding slot in the terminal block retainer. A back plate is attached to the terminal block retainer to enclose the terminal blocks within the cubicles defined by the partitions. Openings in the lower portion of the back plate match up with the wire openings on the lower portion of each terminal block. The wires leading from the transformer are fed through the back plate opening for insertion into the terminal block.